TITLE: Rubbery bladders from epoxy compositions
United States Patent 4119592
ABSTRACT:
Rubbery bladders are produced by rotational casting a liquid polymer
composition containing (1) an epoxy resin, (2) a liquid
carboxyl-terminated polymer, (3) an amine, (4) a dihydric compound, and
(5) a plasticizer. In order to obtain the desired flex and tear
properties, the equivalent ratio of the other reactants to epoxy must
be from about 0.70 to about 1.15. The valve area of the bladder is
reinforced with a spun bonded fabric.
INVENTORS:
Murphy, Walter Thomas (Cuyahoga Falls, OH)
APPLICATION NUMBER: 05/772047
PUBLICATION DATE: 10/10/1978
FILING DATE: 02/25/1977
ASSIGNEE: The B. F. Goodrich Company (Akron, OH)
PRIMARY CLASS: 523/400
OTHER CLASSES: 264/275, 264/311, 264/331.12, 473/609, 523/455, 525/530, 528/94,
528/97, 528/99, 528/103.5, 528/112
INTERNATIONAL CLASSES: C08L7/00; B29B15/00; B29C41/00; B29D22/02; B29D99/00; C08G59/00;
C08G59/40; C08G59/62; C08K5/13; C08K5/3445; C08L13/00; C08L21/00;
C08L23/02; C08L33/08; C08L47/00; C08L63/00; B29C41/04; (IPC1-7):
C08G59/42
FIELD OF SEARCH: 260/836, 260/837R, 260/47EP, 260/47EC, 260/30.4A, 260/30.4EP,
260/31.8E, 260/29.1SB, 260/18PF, 260/78.41, 273/65B
US PATENT REFERENCES:
4028432 Process for manufacturing flexible epoxide resins June, 1977
Dawans et al. 260/836
4025578 Elastomeric liquid polymer vulcanizates from epoxy resin,
liquid carboxy terminated polymer, dihydric phenol, and an amine May,
1977 Siebert 260/837R
4016022 Low flow, vacuum bag curable prepreg material for high
performance composite systems April, 1977 Browning et al. 156/285
3686359 CURABLE POLYEPOXIDE COMPOSITIONS August, 1972 Soldatos et al.
260/836
3673274 POLYMERIC ADHESIVE CONTAINING A POLYEPOXIDE, A CARBOXY
TERMINATED POLYBUTADIENE AND A BIS-2-OXAZOLINE June, 1972 Tomalia et
al. 260/836
OTHER REFERENCES:
Lee et al., "Handbook of Epoxy Resins", McGraw-Hill, 1967, pp. 10-17.
PRIMARY EXAMINER: Anderson, Harold D.
ASSISTANT EXAMINER: Nielsen E. A.
Attorney, Agent or Firm:
Powell J. A.
Powell Jr., J. H.
CLAIMS:
I claim:
1. A liquid polymer composition comprising:
a. a liquid carboxyl-terminated polymer containing polymerized units of
a vinylidene monomer, siad polymer having from about 1.4 to about 2.6
carboxyl groups per molecule,
b. an epoxy resin having an average number of ##STR4## epoxide groups
per molecule of from about 1.7 to about 2.3, c. a plasticizer,
d. a dihydric compound selected from the group consisting of catechol,
resorcinol, hydroxybenzyl alcohol, bis benzylic alcohol, dihydroxy
napthalene and bisphenols of the formula ##STR5## where R' is selected
from the group consisting of an alkylene group containing 1 to 12
carbon atoms and a bivalent radical containing 1 to 8 atoms of C, O, S,
and/or N, and
e. 2-ethyl-4-methylimidazole; wherein the equivalent ratio of the sum
of reactants a, d, and e, to epoxy is from about 0.70 to about 1.15.
2. A composition of claim 1 having a viscosity less than 2500
centipoises measured at 75° C.
3. A composition of claim 2 wherein the liquid carboxyl-terminated
polymer has an average of about 1.8 to about 2.2 carboxyl groups per
molecule, has a bulk viscosity of from about 10,000 centipoises to
about 600,000 centipoises, and has a polymeric backbone consisting of
carbon-carbon linkages derived from polymerized units of a monomer(s)
selected from the group consisting of (a) monoolefins containing 2 to
about 14 carbon atoms; (b) dienes containing 4 to about 10 carbon
atoms; (c) vinyl and allyl esters; (d) vinyl and allyl ethers, and (e)
acrylates of the formula ##STR6## where R is selected from the group
consisting of alkyl radicals containing 1 to about 18 carbon atoms, an
alkoxyalkyl radical, an alkylthioalkyl radical, and a cyanoalkyl
radical each containing 2 to about 12 carbon atoms, and optionally, a
major amount of a monomer (a) to (e) with a minor amount of a monomer
selected from the group consisting of (f) vinyl aromatics, (g) vinyl
nitriles, (h) methacrylates and ethacrylates, and (i) divinyls and
diacrylates.
4. A composition of claim 3 wherein the epoxy resin is selected from
the group consisting of diglycidyl ethers of dihydric phenols and
diglycidyl ethers of dihydric aliphatic alcohols, and has a bulk
viscosity of from about 200 centipoises to about 1,000,000 centipoises,
an epoxide equivalent weight of from about 150 to about 1,000, and an
average of about 2 epoxide groups per molecule.
5. A composition of claim 4 wherein the dihydric compound is selected
from the group consisting of catechol, resorcinol, hydroxybenzyl
alcohol, bisbenzylic alcohol, dihydroxy naphthalene, methylene
bisphenol, butylidene bisphenol, octylidene bisphenol, isopropylidene
bisphenol, bisphenol sulfide, bisphenol sulfone, bisphenol ether, and
bisphenol amine.
6. A composition of claim 5 wherein the liquid carboxyl-terminated
polymer has an average of about 1.8 to about 2.2 carboxyl groups per
molecule, has a bulk viscosity of from about 30,000 centipoises to
about 200,000 centipoises, and is comprised of about 5 percent to about
40 percent by weight of acrylonitrile, about 1.6 percent to about 3.4
percent by weight of carboxyl, and about 58 percent to about 93 percent
by weight of butadiene, all weights based upon the total weight of the
polymer.
7. A composition of claim 6 comprising:
a. 100 parts by weight of epoxy resin,
b. from about 80 parts by weight to about 180 parts by weight of liquid
carboxyl-terminated polymer per 100 parts by weight of epoxy resin,
c. from about 10 parts by weight to about 130 parts by weight of
plasticizer per 100 parts by weight of epoxy resin,
d. from about 30 parts by weight to about 70 parts by weight of
dihydric compound per 100 parts by weight of epoxy resin,
e. from about 1 part by weight to about 5 parts by weight of
2-ethyl-4-methylimidazole per 100 parts by weight of epoxy resin.
8. A composition of claim 7 wherein the amount of plasticizer is from
about 20 to about 50 parts by weight per 100 parts by weight of epoxy
resin.
9. A composition of claim 8 wherein the amount of dihydric compound is
from about 40 to about 60 parts by weight per 100 parts by weight of
epoxy resin.
10. A composition of claim 9 wherein the amount of
2-ethyl-4-methylimidazole is from about 1.5 to about 3 parts by weight
per 100 parts by weight of epoxy resin.
11. A composition of claim 10 wherein the dihydric compound is
isopropylidene bisphenol.
12. A composition of claim 11 wherein the epoxy resin has an equivalent
weight of from about 180 to about 200.
13. A rubber bladder comprising:
a. a liquid carboxyl-terminated polymer containing polymerized units of
a vinylidene monomer, said polymer having from about 1.4 to about 2.6
carboxyl groups per molecule,
b. an epoxy resin having an average number of ##STR7## epoxide groups
per molecule of from about 1.7 to about 2.3, c. plasticizer,
d. a dihydric compound selected from the group consisting of catechol,
resorcinol, hydroxybenzyl alcohol, bis benzylic alcohol, dihydroxy
naphthalene and bisphenols of the formula ##STR8## where R' is selected
from the group consisting of an alkylene group containing 1 to 12
carbon atoms and a bivalent radical containing 1 to 8 atoms of C, O, S,
and/or N, and
e. 2-ethyl-4-methylimidazole; wherein the equivalent ratio of the sum
of reactants a, d, and e, to epoxy is from about 0.70 to about 1.15.
14. A bladder of claim 13 wherein the liquid carboxyl-terminated
polymer has an average of about 1.8 to about 2.2 carboxyl groups per
molecule, has a bulk viscosity of from about 10,000 centipoises to
about 600,000 centipoises, and has a polymeric backbone consisting of
carbon-carbon linkages derived from polymerized units of a monomer(s)
selected from the group consisting of (a) monoolefins containing 2 to
about 14 carbon atoms; (b) dienes containing 4 to about 10 carbon
atoms; (c) vinyl and allyl esters; (d) vinyl and allyl ethers and (e)
acrylates of the formula ##STR9## where R is selected from the group
consisting of alkyl radicals containing 1 to about 18 carbon atoms, an
alkoxyalkyl radical, an alkylthioalkyl radical, and a cyanoalkyl
radical each containing 2 to about 12 carbon atoms, and optionally, a
major amount of a monomer (a) to (e) with a minor amount of a monomer
selected from the group consisting of (f) vinyl aromatics, (g) vinyl
nitriles, (h) methacrylates and ethacrylates, and (i) divinyls and
diacrylates.
15. A bladder of claim 14 wherein the epoxy resin is selected from the
group consisting of diglycidyl ethers of dihydric phenols and
diglycidyl ethers of dihydric aliphatic alcohols, and has a bulk
viscosity of from about 200 centipoises to about 1,000,000 centipoises,
an epoxide equivalent weight of from about 150 to about 1,000, and an
average of about 2 epoxide groups per molecule.
16. A bladder of claim 15 wherein the dihydric compound is selected
from the group consisting of catechol, resorcinol, hydroxybenzyl
alcohol, bisbenzylic alcohol, dihydroxy naphthalene, methylene
bisphenol, butylidene bisphenol, octylidene bisphenol, isopropylidene
bisphenol, bisphenol sulfide, bisphenol sulfone, bisphenol ether, and
bisphenol amine.
17. A bladder of claim 16 wherein the liquid carboxyl-terminated
polymer has an average of about 1.8 to about 2.2 carboxyl groups per
molecule, has a bulk viscosity of from about 30,000 centipoises to
about 200,000 centipoises and is comprised of about 5 percent to about
40 percent by weight of acrylonitrile, about 1.6 percent to about 3.4
percent by weight of carboxyl, and about 58 percent to about 93 percent
by weight of butadiene, all weights based upon the total weight of the
polymer.
18. A bladder of claim 17 comprising:
a. 100 parts by weight of epoxy resin,
b. from about 80 parts by weight to about 180 parts by weight of liquid
carboxyl-terminated polymer per 100 parts by weight of epoxy resin,
c. from about 10 parts by weight to about 130 parts by weight of
plasticizer per 100 parts by weight of epoxy resin,
d. from about 30 parts by weight to about 70 parts by weight of
dihydric compound per 100 parts by weight of epoxy resin,
e. from about 1 part by weight to about 5 parts by weight of
2-ethyl-4-methylimidazole per 100 parts by weight of epoxy resin.
19. A bladder of claim 18 wherein the amount of plasticizer if from
about 20 to about 50 parts by weight per 100 parts by weight of epoxy
resin.
20. A bladder of claim 19 wherein the amount of dihydric compound is
from about 40 to about 60 parts by weight per 100 parts b weight of
epoxy resin.
21. A bladder of claim 20 wherein the amount of
2-ethyl-4-methylimidazole is from about 1.5 to about 3 parts by weight
per 100 parts by weight of epoxy resin.
22. A bladder of claim 21 wherein the dihydric compound is
isopropylidene bisphenol.
23. A bladder of claim 22 wherein the epoxy resin has an equivalent
weight of from about 180 to about 200.
DESCRIPTION:
BACKGROUND OF THE INVENTION
The production of hollow rubber bladders, such as those used to produce
basketballs and the like, is currently a rather complex process. Rubber
compounds, usually butyl rubber, are compounded at high energy
consumption on a rubber mill or Banbury mixer. This compound is then
calendered to the desired thickness in sheet form. From the rubber
sheet, quarter sections of the bladder are die cut and pieced together
by hand with adhesive and end patches. A valve is inserted and adhered
into the construction. The total construction is then heat cured to
produce a bladder. Because of the adhesive splices, which often form
imperfect seals and poor weight balance, this conventional process
often results in high amounts of defective bladders and excess scrap.
Rotocasting is a process now used to produce playballs from
thermoplastic materials such as polyethylene powders and vinyl
plastisols. Unfortunately, these materials do not have the resiliency
and air retention of rubber and are not suitable for use in basketballs
and the like.
SUMMARY OF THE INVENTION
Rubbery bladders are produced by rotocasting a liquid polymer
composition containing (1) an epoxy resin having two epoxide groups per
molecule; (2) a liquid carboxyl-terminated polymer having from about
1.4 to about 2.6 carboxyl groups per molecule; (3) an amine having
selectivity for a carboxyl-epoxide reaction; (4) a dihydric compound;
and (5) a plasticizer. In order to obtain the desired flex and tear
properties, the equivalent ratio of components reactive with an epoxy
group to epoxy must be from about 0.70 to about 1.15.
DETAILED DESCRIPTION
The composition is first prepared as two storage stable components with
the first component containing the liquid polymer, amine and
plasticizer. The second component contains the epoxy and the dihydric
compound. The two components are mixed together at a temperature of
from about 50° C. to about 100° C. to form the rotocastable
composition. A valve along with a spun bonded fabric to reinforce the
valve area are placed on a pin in the bladder mold prior to charging
the mold with the rotocastable composition. Rotocasting is carried out
at a temperature of from about 110° C. to about 180° C. until the
composition is cured.
The liquid carboxyl-containing polymers have an average of from about
1.4 to about 2.6 carboxyl (--COOH) groups per polymer molecule, and
more preferably from about an average of 1.8 to 2.2 carboxyl groups per
molecule. At least one of the carboxyl groups is located at an end of
the polymer molecule, preferably both so that the polymer is
difunctional. The difunctional polymer molecule then is identified as a
liquid carboxyl-terminated polymer. The polymers have a carboxyl
content of about 1.6 to about 3.4 percent based upon the weight of the
polymer. More preferably, the carboxyl content is from about 2.4 to
about 2.8 percent by weight. The carboxyl content can be determined by
titration of a polymer solution to a phenolphthalein end point using
alcoholic KOH.
The liquid carboxyl-containing polymers have a molecular weight of from
about 1,000 to about 8,000 as measured using a Mechrolab Vapor Pressure
Osmometer. The polymers are more conveniently described by their bulk
viscosity. The polymers have a bulk viscosity of from about 10,000
centipoises to about 600,000 centipoises (measured at 27° C. using a
Brookfield Model LVT Viscometer with spindle No. 7 at 0.5 to 100 rpm)
and more preferably from about 30,000 to about 200,000 centipoises.
The carboxyl-containing polymers have polymeric backbones comprising
carbon-carbon linkages. The polymers are elastomers in a cured state.
Polymers having carbon-carbon linkages contain polymerized units of a
vinylidene monomer(s) selected from (a) monoolefins containing 2 to 14
carbon atoms such as ethylene, propylene, isobutylene, 1-butene,
1-pentene, 1-hexene, 1-dodecane and the like; (b) dienes containing 4
to about 10 carbon atoms such as butadiene, isoprene,
2-isopropyl-1,3-butadiene, chloroprene, and the like; (c) vinyl and
allyl esters such as vinyl acetate, vinyl propionate, allyl acetate,
and the like; (d) vinyl and allyl ethers such as vinyl methyl ether,
allyl methyl ether, and the like; and (e) acrylates of the formula
##STR1## wherein R is an alkyl radical containing 1 to 18 carbon atoms
or an alkoxy alkyl, an alkylthioalkyl, or cyanoalkyl radical containing
2 to 12 carbon atoms. Examples of such acrylates are ethyl acrylate,
butyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, dodecyl
acrylate, octadecyl acrylate, methoxyethyl acrylate, butoxyethyl
acrylate, hexylthioethyl acrylate, β-cyanoethyl acrylate, cyanooctyl
acrylate, and the like. Often two or more types of these polymerized
monomeric units are contained in the polymeric backbone.
The vinylidene monomers listed above are readily polymerized in major
amounts with minor amounts of (f) vinyl aromatics such as styrene
α-methyl styrene, vinyl toluene, and the like; (g) vinyl nitriles such
as acrylonitrile, methacrylonitrile, and the like; (h) methacrylates
and ethacrylates such as methyl methacrylate, ethyl methacrylate, octyl
methacrylate, ethyl ethacrylate, and the like; and (i) divinyls and
diacrylates such as divinyl benzene, divinyl ether, diethylene glycol
diacrylate, and the like. Liquid carboxyl-containing polymers comprised
of a vinylidene monomer(s) listed in (a) to (e) with a minor amount of
a vinylidene monomer(s) listed in (f) to (i) are within the scope of
this invention.
The preferred liquid carboxyl-containing polymers are
carboxyl-terminated polymers. Examples of liquid carboxyl-terminated
polymers are carboxyl-terminated polyethylene, carboxyl-terminated
polybutadiene, carboxyl-terminated polyisoprene, carboxyl-terminated
poly(butadieneacrylonitrile), carboxyl-terminated
poly(butadiene-styrene), carboxyl-terminated
poly(butadiene-acrylonitrile-acrylic acid), carboxyl-terminated
poly(ethyl acrylate), carboxyl-terminated poly(ethyl acrylate-n-butyl
acrylate), carboxyl-terminated poly(n-butyl acrylate-acrylonitrile),
carboxyl-terminated poly(butyl acrylate-styrene), and the like. The
polymers can be prepared by free-radical polymerization using
carboxyl-containing initiators and/or modifiers as disclosed in U.S.
Pat. No. 3,285,949, and by solution polymerization using lithium metal
or organometallic compounds and post-treating the polymers to form
carboxyl groups as disclosed in U.S. Pat. Nos. 3,135,716 and 3,431,235.
Carboxyl-terminated poly(butadiene-acrylonitrile) polymers were found
to be especially useful. These polymers contain about 5% to about 40%
by weight of acrylonitrile, about 1.6% to about 3.4% by weight of
carboxyl, and about 58% to about 93% by weight of butadiene based upon
the weight of the polymer. Liquid carboxyl-terminated
poly(butadiene-acrylonitrile) polymers containing from about 8% to
about 20% by weight of acrylonitrile have been found to be excellent
polymers for rotocasting rubber bladders.
The level of liquid carboxyl-terminated polymer used is from about 80
to about 180 parts by weight per 100 parts by weight of epoxy.
Preferably, the level is from about 100 to about 130 parts by weight
per 100 parts by weight of epoxy resin.
The epoxy resin must have an average number of epoxide ##STR2## groups
per molecule of from about 1.7 to about 2.3. An epoxy resin having
substantially above or below this range of epoxide groups per molecule
will not function to prepare the unique rubbery bladders of this
invention. It is believed that epoxy resins having substantially below
an average of 1.7 epoxide groups per molecule do not undergo
chain-extension and/or crosslinking sufficiently enough, and epoxy
resins having substantially above 2.3 epoxide groups per molecule
undergo too much crosslinking to prepare the unique rubbery bladders.
The epoxy resins are liquids having a bulk viscosity (measured using a
Brookfield LVT Viscometer, spindle No. 7, at 0.5 to 100 rpm, at 25° C.)
of from about 200 centipoises to about 1,000,000 centipoises, and more
preferredly from about 500 centipoises to about 300,000 centipoises.
The epoxy resins can have epoxide equivalent weights of from about 150
to about 1,000. More preferredly, the resins have epoxide equivalent
weights of from about 160 to about 400. The epoxide equivalent weight
is the weight of epoxy resins that contains one gram equivalent of
epoxy groups. The epoxide equivalent weight can be determined by using
the pyridium chloride-pyridine method of determining epoxy content.
Many types of epoxy resins can be used. Examples of types are the
diglycidyl ethers of dihydric phenols, the diglycidyl ethers of
dihydric aliphatic alcohols, the diglycidyl ethers of cyclo dihydric
aliphatic alcohols, the diglycidyl esters of dicarboxylic acids, the
diamine compounds substituted by glycidyl radicals, and diepoxidized
fatty acids. Examples of each of these types of epoxy resins are
disclosed in U.S. Pat. Nos. 3,655,818 and 3,678,131. The epoxy resins
can be halogenated.
The diglycidyl ethers of dihydric phenols and the diglycidyl ethers of
dihydric aliphatic alcohols are the more preferred epoxy resins. An
example of the diglycidyl ethers of dihydric phenols are the Bisphenol
A/epichlorohydrin type resins such as the "EPON" resins marketed by
Shell Chemical and the "D.E.R." resins marketed by Dow Chemical. An
example of the diglycidyl ethers of dialiphatic alcohols are the
ethylene glycol/epichlorohydrin type resins marketed by Dow Chemical as
the "D.E.R." 700 Series resins. Properties of these two more preferred
types of epoxy resins are given in the bulletin, Dow Epoxy Resins,
170-140C-5M-267. As mentioned above, although the epoxy resins used can
have an average epoxide content from 1.7 to 2.3 epoxide groups per
molecule, the most preferred epoxy resins have an average of about 2
epoxide groups per molecule.
The amine used is 2-ethyl-4-methylimidazole. The level of amine used is
from about 1 to about 5 parts and more preferably, from about 1.5 to
about 3 parts by weight per 100 parts by weight of epoxy resin.
The dihydric compound used is a dihydric aromatic compound. Examples of
dihydric aromatic compounds are catechol, resorcinol, hydroxybenzyl
alcohols, bis benzylic alcohol, dihydroxy-naphthalenes, and the like,
and bisphenols of the formula ##STR3## where R' is an alkylene group
containing 1 to 12 carbon atoms or a bivalent radical containing 1 to 8
carbon atoms of C, O, S, and/or N. Examples of the bisphenols are
methylene bisphenol, butylidene bisphenol, octylidene bisphenol,
isopropylidene bisphenol, bisphenol sulfide, bisphenol sulfone,
bisphenol ether, bisphenol amine, and the like.
The level of dihydric compound used is from about 30 to about 70 parts
by weight per 100 parts by weight of epoxy resin. The preferred level
is from about 40 to about 60 parts by weight per 100 parts by weight of
epoxy resin.
Plasticizers used are those well known in the art. Suitable
plasticizers are petroleum oils, castor oil, glycerin, silicones,
aromatic and paraffinic oils, and the like; and esters such as alkyl
and aromatic phthalates, sebacates, trimellitates, and the like; and
monoepoxides such as octyl epoxytallate, epoxidized soybean oil and the
like. Preferred plasticizers are di-2-ethylhexyl azelate,
2,2,4-trimethyl-1,3-pentanediol, diisobutyrate and an aromatic
pretroleum distillate having a boiling point of 275° C. and sold under
the trade name of Kenplast G. The level of plasticizers used is from
about 10 to about 130 parts by weight and preferably from about 20 to
about 50 parts by weight per 100 parts by weight of epoxy resin.
Plasticizers are used to lower the viscosity of the liquid polymer
component and the resultant two-component mix and, therefore, the level
used will depend on the selection of the polymer and other ingredients.
In order to obtain the desired flex and tear properties of the liquid
polymer composition, the equivalent ratio of reactants to epoxy must be
from about 0.70 to about 1.15 and preferably from about 0.90 to about
1.10. The reactants are those materials in the composition which react
with the epoxy, i.e., the carboxyl groups of the liquid polymer, amine
groups and the OH groups of the dihydric compound. The equivalent
weight of the epoxy resin is determined by dividing the number of
epoxide groups per molecule into the molecular weight of the epoxy
resin. The equivalent weight of the liquid polymer is determined by
dividing the number of carboxyl groups per molecule into the molecular
weight of the polymer. The equivalent weight of the dihydric compound
is determined by dividing the number of hydroxyl groups per molecule
into the molecular weight of the dihydric compound. The equivalent
weight of 2-ethyl-4-methylimidazole is determined by dividing its
molecular weight by two. 2-ethyl-4-methylimidazole is shown to be
difunctional by Farkas and Strohm, Journal of Applied Polymer Science,
Vol. 12, pp. 159-168 (1968). To determine the equivalent ratio, divide
the number of equivalents of epoxy used into the sum of equivalents
used of the liquid polymer, amine and dihydric compound.
In addition to the essential ingredients, i.e., the epoxy resin, the
liquid polymer, the dihydric compound, amine and plasticizer, the
liquid polymer composition can contain a broad range of compounding
ingredients. These ingredients are typical ingredients used in rubber
and/or epoxy compounding. Standard levels of these ingredients are
employed, such levels being well known in the art. The only limitation
placed on the levels of compounding ingredients used is that the liquid
polymer composition containing these ingredients must be castable at
temperatures ranging from about 50° C. to about 100° C. The amount of
ingredients must be limited so that the viscosity of the liquid polymer
composition is less than about 2500 centipoises measured at 75° C. This
limitation is needed in order to allow the composition to be rotocast.
This relatively low viscosity is required to rotocast articles with
thin walls of 50 mils or less.
Examples of compounding ingredients are carbon black, metal carbonates
and silicates, colorants, metal oxides, antioxidants, and stabilizers.
The essential ingredients, i.e., the liquid polymer, the epoxy, the
amine, the dihydric compound, and the plasticizer are first prepared as
two storage stable liquid components. The first component contains the
liquid polymer, the amine, and the plasticizer. The second component
contains the epoxy and the dihydric compound. Each component is first
mixed separately using mixing kettles, Henschel mixers, ink mills and
the like, employing standard mixing procedures and techniques. Heating
of the materials is helpful to obtain dissolution and uniform
dispersion of the materials. The two components are mixed together and
maintained at a temperature of from about 50° C. to about 100° C. The
viscosity of the composition must be less than about 2500 centipoises
at 75° C. in order to be rotocast to thin walls of 50 mils or less. A
pneumatic valve housing is placed on a pin in the rotocast mold. The
liquid polymer composition is then poured or injected into the rotocast
mold. The mold is heated while rotated to a temperature of from about
110° C. to about 180° C., preferably from about 150° C. to about 170°
C. Once the composition is in the rotocast mold, the viscosity of the
composition should remain substantially unchanged for about 3 to 7
minutes in order to allow the material to paint the walls of the mold
so as to produce a uniform product. As is typical of a rotational
molding process, the mold is rotated about two axes simultaneously. The
ratio of speeds about the major and minor axis is chosen to match the
shape of the mold. The heated mold is rotated for a time sufficient to
cure the composition, which is from about 10' to about 40'. The curing
time is dependent upon the mold temperature and the selection of
ingredients. Once the composition has been cured, the mold is cooled
and the cured bladder is removed from the mold. A check valve assembly
is then inserted into the valve housing.
In order to prevent tearing of the cured bladders upon insertion of the
valve assembly into the valve housing, it is preferred to reinforce the
valve area of the bladder with a spun bonded fabric. The size of the
fabric used should be at least slightly larger in diameter than the
valve housing, and preferably about 1.5 to 2 times the diameter of the
valve housing. In a basketball bladder, a 3.5 inch diameter disk of
spun bonded fabric was found to be useful. The spun bonded fabric is
centered on a pin in the mold and the valve housing is placed
thereafter on the same pin in the mold before injecting the polymer
composition. During the rotocasting process, the composition
impregnates and encapsulates the spun bonded fabric to form a
reinforcement in the valve area. Particularly useful spun bonded
fabrics are spun bonded polyester fibers sold by DuPont as Reemay and
nylon spun bonded fibers sold by Monsanto as Cerex.
The following examples are presented to more fully describe the
invention.
EXAMPLES
General Mixing Procedure
The materials in the first component, i.e., the liquid polymer, the
amine, and the plasticizer are placed into a mixing kettle. A vacuum is
employed while stirring to remove entrapped air. The temperature of
mixing is about 75° C. The materials are mixed until they are uniform,
about 10 to 15 minutes. The materials in the second component, i.e.,
the epoxy and the dihydric compound are placed in a second mixing
kettle. A vacuum is employed while stirring to remove entrapped air.
Temperature of mixing the second component is about 100° C. The
materials are mixed until they are uniform, about 20 to 40 minutes. The
first and second components are then mixed together at a temperature of
75° C. for about 2 to 4 minutes. A vacuum is used while stirring to
remove entrapped air. The viscosity of the total mixture at this point
must be less than 2500 centipoises at 75° C. to obtain a 50 mil or less
wall thickness. The total mixture is than placed in the rotocast mold
and the mold is heated and rotated until the liquid polymer is cured.
The mold is then cooled and the cured bladder is removed from the mold.
EXAMPLE I
This example is presented to show the change in flex and tear
properties of the liquid rubber composition with various reactant/epoxy
equivalent ratios. A liquid carboxyl-terminated
poly(butadiene-acrylonitrile) rubber is mixed with a plasticizer and an
amine to provide the first component. The rubber, identified as CTBN,
has an acrylonitrile content of 10% by weight and a carboxyl content of
2.47% by weight, both weights based upon the total weight of the
polymer, and having a bulk viscosity at 27° C. of 50,000 and a
molecular weight of about 3,500. The polymer has an equivalent weight
of about 1724. The plasticizer is an aromatic petroleum distillate
having a boiling point of 275° C. and sold under the trade name of
Kenplast G. The amine is 2-ethyl-4-methylimidazol and has an equivalent
weight of 55. The first component is mixed at 75° C. following the
general mixing procedure. An epoxy is mixed with a dihydric compound to
provide the second component. The epoxy, identified as Epon 828, which
is a bisphenol A-epichlorohydrin type resin having two terminal epoxide
groups, an equivalent weight of about 190, and a bulk viscosity at 25°
C. of about 12,000 centipoises. The dihydric compound, identified as
BPA, is p,p'-isopropylidene bisphenol and has an equivalent weight of
114. The second component is mixed at 100° C. following the general
mixing procedure. The two components are mixed at a temperature of 75°
C. for about 2 to 4 minutes. A vacuum is used while stirring to remove
entrapped air. The samples are cast into test specimen molds and the
molds heated for 30 minutes at 160° C. to cure the samples. Table I
lists the compositions, reactant/epoxy equivalent ratio, and the test
results of each composition.
TABLE I
_______________________________________________________________________
___
SAMPLE
_______________________________________________________________________
___
INGREDIENT - PARTS BY WEIGHT
A B C D E
_______________________________________________________________________
___
CTBN 120 120 128 145 163
Kenplast G 30 30 32 36 41
2-ethyl-4-methylimidazol
2 2 2.2 2.33 2.5
EPON 828 100 100 100 100 100
BPA 24 40 50 50 50
Reactant/epoxy equivalent ratio
0.60 0.87 1.05 1.07 1.10
TEST RESULTS
Tensile (psi) 2410 2455 1160 1060 875
100% modulus (psi) 1370 1040 400 30 205
Percent Elongation 145 170 260 355 460
Shore A hardness 76 74 72 69 65
Tear die c lbs./inc.
75 99 107 138 137
de Mattia flex-no. of flex at failure × 1000
0.5 6.2 25 60 610
_______________________________________________________________________
___
This example shows that when the reactant/epoxy equivalent ratio is
increased as in Samples B, C, D, and E, the tear strength of the
composition is greatly increased. The resistance to flex fatigue of
Samples B, C, D, and E with the higher equivalent ratio is dramatically
improved as compared to Sample A with the lower equivalent ratio.
EXAMPLE II
A basketball bladder is produced as follows: The composition of Sample
D in Example I is prepared according to the general mixing procedure.
After placing a pneumatic valve housing on a pin in the rotocast mold,
170 grams of the two-component mixture, having a viscosity of 1700
centipoises at 75° C., is poured into the mold. The mold is heated and
rotated at a 4:1 ratio for 20 minutes at 160° C. The mold is cooled to
about 40° C., and the cured basketball bladder is removed from the
mold. A check valve assembly is inserted into the valve housing to
complete the bladder process. The bladder produced is suitable for
further processing into a basketball which would normally involve
filament winding a fabric onto the bladder and then applying a suitable
cover to produce the final product.
EXAMPLE III
A basketball bladder is made as in Example II, except prior to placing
the pneumatic valve housing onto the pin in the rotocast mold, a 3.5
inch diameter disk of spun bonded polyester fiber, identified as DuPont
Reemay Style 2033, is centered on the pin in the mold. During
rotocasting the liquid polymer composition impregnates the the fabric
and forms a reinforcement in the valve housing area. The reinforcement
in the valve area is especially useful because as the check valve
assembly is inserted into the valve housing there is a likelihood of
tearing the bladder in the valve area. A bladder produced with the spun
bonded fabric in the valve area is greatly improved for tear in the
valve area.
Rubbery bladders produced by this invention have many uses, such as to
produce basketballs and other sport balls. The novel rubbery
compositions of this invention possess good tear strength and excellent
resistance to flex fatigue.